The universal serial bus (USB) is a transmission standard developed in 1994, it supports plug and play as well as hot plugging, and allows removal or unplugging of a device without the need of executing complicated applications. The USB also enables higher transmission rate than other types of buses, and is therefore more convenient for use compared to other buses.
The USB has already become a main specification for transmission. Currently, almost all kinds of computer peripherals, such as external hard drives, printers, mice, keyboards and so on, use a USB connector to connect with a computer. The USB interface provides a uniform connector for various peripherals, including power supply interfaces, communication interfaces, video output devices, audio input devices, data storage devices and the like. All these devices use the same USB interface specifications. However, since most currently available peripherals use USB sockets and plugs, the USB ports provided on a computer host, such as the desktop computer host or the notebook computer host, are not sufficient in number now.
To solve the problem of insufficient USB ports on computers, there is developed a USB hub, to which more devices can be connected. The USB hub has a unit electrically connected to a USB plug and a plurality of USB ports. When the USB plug is plugged in a USB port on a host system, such as a computer host, power can be supplied to all the USB ports of the USB hub from the computer, so that multiple peripherals can be connected to the USB ports on the USB hub to solve the problem of insufficient USB ports on the computer host.
Another fact is that more and more battery-powered portable devices have been developed in recent years, such as smartphones, MP3/4/5, tablet computers, power banks, card readers, digital cameras and so on. Users usually wish to use these portable devices to transmit data at any time and any place while charging the devices synchronously.
However, the conventional USB hub is mainly designed to provide more USB ports for connecting more devices to a host system via the USB hub, so that these devices can work with the computer host to enable data transmission between them at the same time. The conventional USB hub must be connected to a power supply inside the computer to obtain required power for maintaining its normal operation. That is, the conventional USB hub itself does not provide any power source for operating independently. In the case too many devices are connected to the ports on the USB hub, the USB hub would encounter the condition of insufficient voltage, which would cause difficulties in data transmission, data storage or device charging. In worse conditions, the computer system might be overloaded and become crashed, and the USB hub would also become damaged.
To overcome the above problems, there is developed an external USB hub that can be connected to an AC wall outlet that supplies mains electricity. Since the USB hub must be externally connected to the conventional AC wall outlet for use, it is subjected to damaged pins due to frequent plugging and unplugging of the pins into and from the AC wall outlet. Further, the currently commercially available USB hub externally connected to the AC wall outlet is raised from a cover plate of the AC wall outlet and accordingly, would cause inconvenience in use.
It is therefore desirable to develop an improve USB hub, which can be provided with sufficient power supply to avoid damage thereto and has an appearance design that is esthetic and allows convenient use of the USB hub.